Surface defects related to polishing cycle in beta-Ga2O3 crystals grown by floating zone

We report an investigation on beta-Ga2O3 Schottky barrier diodes performed on substrates grown by floating-zone method using structural characterization techniques (secondary-ion mass spectrometry, inductively coupled plasma-mass spectroscopy, and atomic force microscopy) and electrical measurements (current-voltage, capacitance-voltage, Hall effect, and capacitance deep-level transient spectroscopy). Four distinct electron trap levels labeled ES, E1, E2, and E3 were found in the range of 1 eV below the Ga2O3 conduction band minimum. Among them, E1, E2, and E3 show signatures similar to those reported in the literature for Czochralski and edge-defined film-fed grown beta-Ga2O3 substrates. Trap ES was found near the surface, and we could establish a link between this defect and the damage induced by the substrate polishing technique. The level related to ES was identified at similar to 0.31 eV below the conduction band minimum. An energy band above 0.31 eV was also detected and is associated with states at the metal-semiconductor interface. We demonstrated that the interface states and surface deep traps are not uniformly distributed on the beta-Ga2O3 surface. Furthermore, they contribute to the reverse leakage current and the on-state conduction degradation of the diodes.